And I'm David Greene at member station WLRN in Miami. Homeland Security Secretary Jeh Johnson is in southern Arizona today along the border with Mexico. He'll be touring facilities where the government has been processing a large number of children from Central America who've been arriving illegally. These are stunning numbers. More than 50,000 children traveling without adults have been apprehended along the border in the last nine months. It's a huge humanitarian challenge for the Obama Administration. As NPR's Scott Horsley reports, it's a political challenge as well.

SCOTT HORSLEY, BYLINE: Secretary Johnson's trip to Arizona is the latest move by the Administration to address what it concedes as a big and growing problem. The White House initially blamed the wave of migrant youngsters on mounting gang violence and poverty in Central America. But Republican Congresswoman Candice Miller of Michigan argues those conditions are nothing new.

CONGRESSMAN CANDICE MILLER: To say that that's a reason that we suddenly have tens of thousands of children, children traveling thousands of miles through Mexico - all the way up through Mexico - and then illegally entering the United States simply isn't true. I think that this humanitarian crisis can be laid directly at the feet of President Obama as a result of his policy in 2012.

HORSLEY: That policy, adopted in the run-up to the president's re-election, allows immigrants who were brought to the country illegally as children to remain in the U.S. But only if they arrived here by 2007. The policy offers no protection to children entering the country illegally today. Still, Secretary Johnson acknowledges some new arrivals may have been misled.

JEH JOHNSON: I do believe that the smuggling organizations are putting out a lot of disinformation about the conditions - the legal conditions - here in the United States to induce this activity.

HORSLEY: The Administration is now belatedly trying to get the word out to families in Central America not to send their children North. Vice President Biden traveled to Guatemala last week where he delivered a blunt warning that young migrants will not be allowed to stay.

VICE PRESIDENT JOE BIDEN: Make no mistake. Once an individual's case is fully heard and if he or she does not qualify for asylum, he or she will be removed from the United States and returned home.

HORSLEY: Biden also promised tens of millions of dollars in aid to Guatemala, Honduras and El Salvador to combat gang violence and promote economic opportunities. But even as the Administration tries to stem the tide of future migrants, it's struggling to cope with tens of thousands of young Central Americans who are already here. They've far outgrown the government's existing facilities and officials are scrambling to lease additional space. White House spokesman Josh Earnest says the Administration's also bringing on extra attorneys and immigration judges to speed up the deportation process.

JOSH EARNEST: We have taken a number of steps to surge resources to try to address this problem, both in a way that reflects the humanitarian situation, but also in a way that reflects our nation's commitment to being a nation of laws.

HORSLEY: It's a familiar predicament for the White House, as it tries not to alienate either the Latino voters who helped elect the president, or the border enforcement hawks whose support is needed for immigration reform. So far, most of the criticism aimed at the White House is from Republicans. But even some Democrats, like Arizona Congressman Ron Barber, say they feel blindsided.

CONGRESSMAN RON BARBER: Firstly, nobody in Arizona knew that these children were coming. I found out about it through the newspaper. The local sheriff found out about it the same way.

HORSLEY: House Speaker John Boehner accused the president of failing to address the crisis. And he set up his own Republican working group to make recommendations. Boehner has urged Obama to mobilize the National Guard for help, though Secretary Johnson argues more boots on the border won't help.

JEH JOHNSON: You have to realize these kids probably want to get caught. They will run to the nearest officer and say here I am. So you have to ask, will an increased border presence deter that?

HORSLEY: White House spokesman Earnest notes the immigration overhaul bill passed by the Senate last year actually includes additional border enforcement. But with a war of words in Washington, and with hundreds of migrant children turning themselves into the border patrol each day, any such broad overhaul seems more of a long-shot than ever. Scott Horsley, NPR News, Washington. Transcript provided by NPR, Copyright NPR.